Many organizations have offices that are geographically dispersed. To provide communication between offices, the organizations often rent dedicated lines from the telephone company or other communication providers. For example, "T1" lines may be leased from local telephone companies in the United States. T1 lines have a band width of 1.544 MB. In Europe, "E1" 2.048 MB(PCM-30) lines serve a similar function.
The interface circuits at each end of such a communication line convert data input thereto to one of a number of formats for transmission over the T1 line. The communication format provides error correction and other features that insure that data will be transmitted with a minimum of errors while maintaining as high a through-put as possible. "Packaging" of data into frames with error encryption data that allows the receiver to correct errors that occur in transmission is well known to those in the communication art and hence will not be discussed in detail here. For the purposes of the present discussion, it is sufficient to note that there are a number of different packaging options.
In addition, long distance communication requires the use of repeaters to compensate for power lost during transmission. These repeaters must remain in synchronization with each other. One method for maintaining synchrony relies on the transitions between ones and zeros in the data stream being transmitted. This scheme requires a minimum density of ones in the data stream to maintain synchronization of the repeaters. To guarantee that the minimum density is used, various coding schemes insert data into the frames. The precise scheme used, in general, depends on the provider of the T1 line.
From the foregoing discussion, it will be apparent that there are a large number of possible transmission protocols that must be accommodated by the interface devices. Furthermore, to provide a communication interface, the devices at each end of the communication link must use matching protocols.
In principle, the protocols used at each end of the communication link are synchronized at the time the communication link is set up and the interface devices installed. However, even if the devices are correctly configured when the communication link is installed, the replacement of one of the devices or a loss of configuration information in one of the devices due to a power failure and/or transients can lead to a situation in which one of the devices must be reconfigured to match the other device on the communication link.
If the device requiring re-configuration is not at a location that is proximate to qualified service personnel, the reconfiguration can be costly, as a service person must be dispatched to make the required changes. In addition, even if personnel are available on site, it would be advantageous to provide a system in which the device requiring reconfiguration can be configured by the device at the other end of the communication link.
Broadly, it is the object of the present invention to provide an improved communication interface for PCM-24/T1 or PCM-30 communication links.
It is a further object of the present invention to provide an interface for PCM-24/T1 or PCM-30 communication links that can be configured from a remote location.
These and other objects of the present invention will become apparent to those skilled in the art from the following detailed description of the invention and the accompanying drawings.